Master cylinder

ABSTRACT

A master cylinder has a housing with a bore therein having a tapered section located between first and second compensator ports connecting the bore to a reservoir. A sleeve locates first and second lip seals adjacent the first and second compensator ports, respectively. A first piston engages the first lip seal and a second piston engages the second lip seal to define first and second chambers within the bore. A bearing member which surrounds the first piston engages the sleeve and holds the first and second lip seals in a stationary position within the bore. Thereafter, an input member moves the first and second pistons past the first and second lip seals to pressurize the fluid in the first and second chambers and provides fluid pressure responsive devices with an operational input through first and second outlet ports in the housing.

This is a .Iadd.Reissue of U.S. Pat. No. 4,249,381, which is a.Iaddend.continuation of application Ser. No. 890,757, filed Mar. 27,1978, now abandoned.

BACKGROUND OF THE INVENTION

The manufacture of master cylinders is usually achieved through eithersand or permanent mold casing of molten metal to a particular shape.When the molten metal has cooled the sand or core is removed from anycavities therein. As the molten metal cools, a uniform dense surface iscreated on the periphery of the casting; however, some voids may occurinternally. Thereafter when the casting is machined to its finaltolerance, such as the master cylinder housing disclosed in U.S. Pat.No. 3,701,257, it is possible that some of the voids may be exposed inthe pressurizing chambers. If a master cylinder were assembled having avoid exposed in the bore, in addition to providing a possible leak pathfor the high pressure fluid in the pressurizing chamber, it is possibleto damage the seals as they are moved past such voids. Thus once a voidis exposed in the bore through machining for safety, the master cylindercasting is automatically scrapped. It is estimated that between 2 and 5percent of the castings manufactured during any given period of time arescrapped because of the potential hazards created by the exposure ofvoids during machining.

It has been observed that die casting, when compared with sand orpermanent mold castings, produces a smoother surface finish with thinnerdimensions and closer manufacturing tolerances.

SUMMARY OF THE INVENTION

I have devised a master cylinder having a die cast housing with a pistonarrangement therein which eliminates the need for machining theoperational bore and thereby reduces the scrap rate and machining costin the manufacturing of a master cylinder.

The master cylinder housing has a sleeve which locates first and secondlip seals adjacent the first and second compensator ports to establishan effective operational diameter of the bore. A first piston engagesthe first lip seal and a second piston engages the second lip seal toestablish first and second chambers within the bore. A bearing memberwhich surrounds the first piston engages the sleeve and holds the firstand second lip seals in substantially a stationary position. An inputforce applied to the first piston moves the first and .[.secnd.]..Iadd.second .Iaddend.pistons past the first and second lip seals,respectively, to seal the first and second chambers from the reservoirand allow pressurized fluid to be communicated to a fluid pressureresponsive device.

When the input force terminates, a return spring arrangement moves thefirst and second pistons toward a rest position to allow freecommunication between the first and second chambers through thecompensator port to the reservoir. To assure such free communication,the first and second lip seals have a plurality of grooves on theexternal surfaces thereof and the first and second pistons have acorresponding plurality of fluted surfaces to establish a positive flowpath through which fluid is communicated to the first and secondchambers.

It is therefore an object of this invention to provide a master cylinderhaving a die cast surface with a piston arrangement to pressurize thefluid therein in response to an operator input force.

It is a further object to provide a master cylinder having a taperedoperational bore therein with a piston arrangement through which fluidis pressurized and supplied to a fluid pressure responsive device.

These and other objects should be apparent from reading thisspecification and viewing the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a brake system having a sectionalview of a master cylinder made according to the principles of thisinvention;

FIG. 2 is an exploded perspective view of the piston assembly of themaster cylinder of FIG. 1;

FIG. 3 is a sectional view of circumscribed line 3 of FIG. 1 showing therelationship between the sleeve, lip seal, primary piston and bearingmember of the piston assembly in a released position;

FIG. 4 is a sectional view taken along line 4--4 of FIG. 3; and

FIG. 5 is a sectional view of circumscribed line 3 of FIG. 1 showing therelationship between the sleeve, lip seal, primary piston and bearingmember of the piston assembly in an operational position.

DETAILED DESCRIPTION OF THE INVENTION

In the brake system 10 shown in FIG. 1, a master cylinder 12 isconnected to the front wheel brakes 14 and the rear wheel brakes 16 byconduits 18 and 20.Iadd., .Iaddend.respectively. In response to anoperational input applied from brake pedal 22 through push rod 24, themaster cylinder 12 is operated to effect a brake application.

In more particular detail, the master cylinder 12 has a die cast housing26 with a bore 28 located therein. Bore 28 has a series of steps 30, 32,34, 36 and 38 which have a slope or taper of about 1° with respect to anaxial plane through bore 28. Such a slope or taper is placed in thehousing during die casting and is necessary to permit the removal of adie cast core after the metal in the housing 26 has cooled from a moltencondition. The housing 26 has a first compensator port 40 and a secondcompensator port 42 through which bore 28 is connected with compartments44 and 46, respectively, in the fluid reservoir.

A piston assembly 48 which is located in bore 28 has a first piston 52and a second piston 54. As shown in FIG. 2, the second piston 54 has acylindrical body 60 with a first diameter and a second diameter. Thecylindrical body 60 has a bore 62 which extends through the firstdiameter and into the second diameter. A series of openings 64, 64',etc., connect the bore 62 with bore 28. A retainer 55 located in bore 62has a stem 66 attached to piston 52 for caging spring 58 and therebyinitially establish a distance between pistons 52 and 54 to establishthe size of a first pressure chamber 56 in bore 28.

Piston 54 has an outwardly projecting lip 70 which engages one end ofspring 59 to hold the second piston 54 away from the bottom of bore 28and establish the size of a second pressurizing chamber 72.

A sleeve member 74 has a first end 76 that engages shoulder 78 to locatea second end 80 adjacent compensator port 42 and a lip seal 115 in step32 of bore 28 to control communication of fluid between chambers 46 and72. Sleeve member 74 has a shoulder 82 that locates O-ring seal 84against shoulder 86 to prevent fluid communication from chamber 56between steps 32 and 34 of bore 28 and a shoulder 88 that positionsO-ring seal 90 against shoulder 92 to prevent fluid communication fromchamber 56 between steps 34 and 36.

Similarly, an O-ring seal 94 located adjacent rib 96 of the sleevemember 74 by spring retainer 98, engages the cylindrical body 60 ofpiston 54 to prevent fluid communication between chambers 56 and 72.

As illustrated in FIGS. 1 and 2, sleeve member 74 has a leg 100 thataligns its cylindrical body 102 within bore 28 to compensate for thetaper or slope in step 34 between the first and second compensator ports40 and 42. Lip 70 engages the interior surface 104 and cylindrical body102 engages bearing surface 106 of rib 96 to align or centrally positionpiston 54 in step 32 of bore 28.

A bearing member 110 which surrounds the cylindrical body of piston 52engages end 76 of sleeve 74 to position a lip seal 114 adjacent leg 100and align passages 112 with compensator port 40 and groove 113 inbearing 110. A seal 116 located in groove 118 of the bearng member 110prevents fluid communication from compensator port 40 to the surroundingenvironment along step 38 of bore 28.

A snap ring or other fastener 140 engages bearing member 110 to hold thepiston assembly 48 within the bore 28.

To assure that bore 28 is communicated with the reservoir, lip seals 114and 115 and pistons 52 and 54 cooperate to define positive flow paths,as shown in FIGS. 3 and 4, between chamber 56 and compartment 42 andchamber 72 and compartment 46, respectively.

Lip seals 114 and 115 are identical with exception of size and thus thespecific detail shown with respect to lip seal 114 in FIGS. 3 and 4 areequally applicable to lip seal 115.

Lip seal 114 has an annular base 120 with legs 122 and 124 attachedthereto. A series of radial grooves 126, only one being shown in FIGS. 3and 4, which are located on the back side 128 of the base 120 provide aflow path from groove 113 in bearing 110 to the cylindrical surface 130of piston 52. A groove 132 on the peripheral surface 134 of leg 122connects the radial grooves 126 with a series of fluted grooves 136 onthe end of the cylindrical surface 130 to define a positive flow pathbetween compartment 44 into chamber 56 to maintain the fluid therein incompletely filled condition.

A cover member .[.140.]. .Iadd.139 .Iaddend.having a cap 142 and adiaphragm 144 is attached to housing .[.260.]. .Iadd.26.Iaddend.. Thediaphragm 144 has a first bead 146 on its peripheral surface and asecond bead 148 which separates the diaphragm 144 into two sections, 152and 154. A first groove 156 is located in the first section 152 and asecond groove 158 is located in the second section 154. The cap 142 hasribs 160 and 162 thereon which are located in grooves 156 and 158 toresiliently bias the diaphragm 144 toward walls 164, 166 and 168 andattach the cover member .[.140.]. .Iadd.139 .Iaddend.to the housing 26and thereby seal compartment 44 and 46 from the surrounding environment.

MODE OF OPERATION OF THE INVENTION

When an operator desires to make a brake application in a vehicleequipped with a brake system as shown in FIG. 1, an input force appliedto pad 23 causes pedal 22 to move in an arc about pin 25 and providepush rod 24 with a linear input. This linear input simultaneously movesthe fluted grooves 136 and 137 on pistons 52 and 54 past grooves 132 and133 as return spring 59 is overcome to interrupt communication betweenchambers 56 and 72 and compartments 44 and 46, respectively. Movement ofpistons 52 and 54 into chambers 56 and 72 causes a fluid pressure toproportionally increase therein and supply wheel brakes 14 and 16 withfluid pressure to effect a brake application.

As shown in FIG. 5, the lip seal 114 remains stationary as piston 52moves into chamber 56 to pressurize the fluid therein. The fluidpressure in chamber 56 acts on lip seal 114 to hold leg 124 againstsleeve 74, surface 128 against bearing 110 and surface 134 of leg 122against the cylindrical surface 130 of piston 52 to prevent fluidcommunication to compartment 44 of the reservoir.

Upon termination of the input force on pedal 22, return spring 59 actson the second piston 54 and moves the first and second pistons 52 and 54toward stop 140. As tips 142 and 144 of fluted grooves 136 and 137 reachgrooves 132 and 133, fluid communication between chambers 56 and 72 andreservoir compartment 44 and 46 is initiated through a defined flow pathestablished by grooves 126 to assure that any fluid which could be lostfrom the brake system is replenished prior to another application ofinput brake force by an operator.

I claim: .[.1. A master cylinder comprising: through said first andsecond outlet ports..].
 2. The master cylinder, as recited in claim.[.1.]. .Iadd.32.Iaddend., wherein said second cylindrical body furtherincludes:a plurality of openings located in said first diameter sectionto allow fluid to freely flow between the tapered bore and the firstchamber with relative movement between the first and second cylindricalmembers.
 3. The master cylinder, as recited in claim .[.1.]..Iadd.32.Iaddend., further including:a wall for separating the reservoirinto first and second compartments; a diaphragm having a first bead onits peripheral surface and a second bead, said first and second beadshaving grooves thereon; and cover means having first and second ribsthereon located in said grooves for biasing said first and second beadsagainst said housing and wall to seal said first and second chambersfrom the surrounding environment.
 4. The master cylinder, as recited inclaim .[.1.]. .Iadd.32.Iaddend., wherein said second cylindrical bodyfurther includes:a second bore that extends through said first diametersection and into said second diameter section, said first spring beinglocated in said bore and said first cylindrical member telescoping intosaid second bore to provide a compact unitary structure.
 5. The mastercylinder, as recited in claim 4, wherein said second cylindrical bodyfurther includes:a plurality of openings located in said first diametersection to allow fluid to freely flow between the second bore and thefirst chamber with relative movement between the first and secondcylinder members.
 6. The master cylinder, as recited in claim 5, furtherincluding:a wall for separating the reservoir into first and secondcompartments; a diaphragm having a first bead on its peripheral surfaceand a second bead, said first and second beads having grooves thereon;and cover means having first and second ribs thereon located in saidgrooves for biasing said first and second beads against said housing andwall to seal said first and second chambers from the surroundingenvironment.
 7. A master cylinder comprising:a housing having a taperedbore therein, said housing having first and second compensator ports forconnecting said tapered bore to a fluid reservoir and first and secondoutlet ports connected to fluid pressure responsive devices; a sleevelocated in said tapered bore; first and second seals located in saidtapered bore, said first and second seals each having a plurality ofradial grooves for establishing definite flow paths between the firstand second compensator ports and the tapered bore.Iadd., said sleeveholding said second seal in a stationary position.Iaddend.; bearingmeans located in said tapered bore for holding said first .[.and secondseals.]. .Iadd.seal .Iaddend.in a stationary position; piston meanshaving first and second cylindrical members located in said tapered boreby said bearing means and .[.engaging.]. said first and second seals,respectively, to define first and second chambers in said tapered boreadjacent said first and second outlet ports, each of said first andsecond cylindrical members having a .[.fluted.]. section located on theend thereof for defining an extension between said definite flow pathand the first and second chambers, .[.said second cylindrical memberhaving a first diameter section and a second diameter section, saidfirst diameter section having a lip on the peripheral surface thereoffor engaging.]. said sleeve .[.to hold.]. .Iadd.holding .Iaddend.saidsecond .[.diameter section.]. .Iadd.cylindrical member .Iaddend.in theaxial center of the tapered bore in the second chamber; and input meansresponsive to an input force for moving the first and second cylindricalmembers past said first and second seals to interrupt communicationbetween the reservoir and the tapered bore through said definite flowpaths and extension thereof to allow further movement of the first andsecond cylindrical members to pressurize the fluid in the first andsecond chambers and thereby supply the fluid pressure responsive deviceswith operational fluid through said first and second outlet ports. . Themaster cylinder, as recited in claim 7 further including:a first springlocated between said first and second cylindrical members to establishthe size of said first chambers; and a second spring located between.[.said.]. .Iadd.a .Iaddend.lip on the first cylindrical member and saidsleeve member for urging said first and second cylindrical members outof said first and second chambers toward a rest position.
 9. The mastercylinder, as recited in claim 8 wherein said second cylindrical bodyfurther includes:a second bore that extends through .[.said.]. .Iadd.a.Iaddend.first diameter section and into .[.said.]. .Iadd.a.Iaddend.second diameter section, said first spring being located insaid second bore and said first cylindrical member telescoping into saidsecond bore to provide a compact unitary structure.
 10. The mastercylinder, as recited in claim 9 wherein said second cylindrical bodyfurther includes:a plurality of openings located in said first diametersection to allow fluid to freely flow between the second bore and thefirst chamber with relative movement between the first and secondcylindrical members.
 11. The master cylinder, as recited in claim 7wherein said sleeve .[.member.]. includes:a plurality of openingsthrough which fluid is communicated to said first outlet port.
 12. Themaster cylinder, as recited in claim 7 wherein said first cylindricalmember telescopes into said second cylindrical member to provide acompact unitary structure. .[.13. A master cylinder comprising:a housinghaving a tapered bore therein, said housing having first and secondcompensator ports for connecting said tapered bore to a reservoir andfirst and second outlet ports; a sleeve located in said tapered bore;first and second seals positioned in said tapered bore adjacent saidfirst and second compensator ports, each of the first and second sealshaving a radial groove therein for defining a definite flow path betweenthe compensator ports and the tapered bore; bearing means engaging saidsleeve to hold said first and second seals in a stationary positionwithin said bore; piston means having first and second cylindricalmembers located in said sleeve and engaging said first and second sealsto define first and second chambers in the tapered bore, said secondcylindrical member having a first diameter section and a second diametersection, said first diameter section engaging said sleeve to hold saidsecond diameter section in the axial center of the tapered bore in thesecond chamber; and input means responsive to an input force for movingthe first and second cylindrical members past said first and secondseals to interrupt communication between the reservoir and the taperedbore through said definite flow paths to allow further movement of thefirst and second cylindrical members to pressurize the fluid in thefirst and second chambers and thereby supply the fluid pressureresponsive devices with operational fluid through said first and secondoutlet ports..].
 14. The master cylinder, as recited in claim .[.13.]..Iadd.33 .Iaddend.further including:a first spring located between saidfirst and second cylindrical members to establish the size of said firstchamber; and a second spring located between said sleeve member and.[.the first diameter section of.]. said second cylindrical member forurging said first and second .Iadd.cylindrical .Iaddend.members out ofthe first and second chambers toward a rest position.
 15. The mastercylinder, as recited in claim 14 wherein said first and secondcylindrical members each include:a fluted section located on the end ofsaid first and second cylindrical members for defining an extensionbetween said definite flow path and the first and second chambers. 16.The master cylinder as recited in claim 15 wherein said secondcylindrical member further includes:a .[.second.]. .Iadd.blind.Iaddend.bore that extends through .[.said.]. .Iadd.a .Iaddend.firstdiameter section and into .[.said.]. .Iadd.a .Iaddend.second diametersection, said first spring being located in said .[.second.]..Iadd.blind .Iaddend.bore and said first cylindrical member telescopinginto said .[.second.]. .Iadd.blind .Iaddend.bore to provide a compactunitary structure.
 17. The master cylinder, as recited in claim 16wherein said second cylindrical body further includes:a plurality ofopenings located in said first diameter section to allow fluid to freelyflow between the .[.second.]. .Iadd.blind .Iaddend.bore and the firstchamber with relative movement between the first and second cylindricalmembers.
 18. A master cylinder comprising:a housing having a steppedbore therein, said housing having first and second inlet ports forconnecting said stepped bore to a reservoir and first and second outletports; .[.a.]. sleeve .Iadd.means .Iaddend.located in said stepped bore;first and second seals positioned in said stepped bore adjacent saidfirst and second inlet ports; bearing means .[.engaging.]..Iadd.cooperating with .Iaddend.said sleeve .Iadd.means .Iaddend.to holdsaid first and second seals in a stationary position within said steppedbore; passage means between said first .[.and second seals.]. .Iadd.seal.Iaddend.and bearing means .Iadd.and said second seal and sleeve means.Iaddend.for defining definite flow paths between the first and secondinlet ports and the stepped bore; piston means having first and secondcylindrical members located in said sleeve .Iadd.means .Iaddend.andengaging said first and second seals to define first and second chambersin the stepped bore, .[.said second cylindrical member having a firstdiameter section and a second diameter section, said first diametersection engaging.]. said sleeve .[.to hold.]. .Iadd.means holding.Iaddend.said second .[.diameter section.]. .Iadd.cylindrical member.Iaddend.in substantially the axial center of the stepped bore in thesecond chamber; and input means responsive to an input force for movingthe first and second cylindrical members past said first and secondseals to interrupt communication between the reservoir and the steppedbore through said definite flow paths to allow further movement of thefirst and second cylindrical members to pressurize the fluid in thefirst and second chambers and thereby supply the fluid pressureresponsive devices with operational fluid through said first and secondoutlet ports.
 19. The master cylinder, as recited in claim 18 furtherincluding:a first spring located between said first and secondcylindrical member to establish the size of said first chamber; and asecond spring located between said sleeve member and .[.the firstdiameter section of.]. said second cylindrical member for urging saidfirst and second members out of the first and second chambers toward arest position.
 20. The master cylinder, as recited in claim 19 whereinsaid first and second cylindrical members each include:a fluted sectionlocated on the end of said first and second cylindrical members fordefining an extension between said definite flow path and the first andsecond chambers.
 21. The master cylinder as recited in claim 20 whereinsaid second cylindrical member further includes:a .[.second.]..Iadd.blind .Iaddend.bore that extends .[.through said.]. .Iadd.from a.Iaddend.first diameter section and into .[.said.]. .Iadd.a.Iaddend.second diameter section, said first spring being located insaid .[.second.]. .Iadd.blind .Iaddend.bore and said first cylindricalmember telescoping into said .[.second.]. .Iadd.blind .Iaddend.bore toprovide a compact unitary structure.
 22. The master cylinder, as recitedin claim 21 wherein said second cylindrical body further includes:aplurality of openings located in said first diameter section to allowfluid to freely flow between the second bore and the first chamber withrelative movement between the first and second cylindrical members..Iadd.
 23. A master cylinder comprising: a housing having a boretherein, said housing having first and second inlet ports for connectingsaid bore to a reservoir and first and second outlet ports; first andsecond pistons located in said bore to define first and second chambers;first and second seals located in said bore for engaging said first andsecond pistons, respectively; a sleeve located in said bore between saidfirst and second seals for guiding said first piston in said bore; abearing member for guiding said second piston in said bore, said bearingmember fixedly positioning said sleeve in said bore and the first sealbetween a shoulder in the bore and a first end of the sleeve and thesecond seal between a shoulder on the sleeve and a first end of thebearing member, said first seal having grooves located adjacent saidfirst end of said sleeve and said second seal having grooves locatedadjacent said first end of said bearing member, to establish a definiteflow path between the reservoir and said first and second chambersthrough said first and second ports, respectively; and an input memberresponsive to an input force for moving said first and second pistonwith respect to said first and second seals to pressurize fluid in saidfirst and second chamber for distribution to said first and secondoutlet ports. .Iaddend..Iadd.
 24. The master cylinder, as recited inclaim 23 wherein, said sleeve means includes: a plurality of openingsthrough which fluid in said second chamber is communicated to saidsecond outlet port. .Iaddend..Iadd.
 25. The master cylinder, as recitedin claim 23, wherein said first and second pistons each include a flutedsection on the end thereof, said fluted section providing an extensionfor said definite flow path to assure free communication between thereservoir and first and second chambers in the absence of an input forceon said input member. .Iaddend..Iadd.
 26. A master cylinder comprising:ahousing having a bore therein, said housing having first and secondinlet ports for communicating said bore with a reservoir and first andsecond outlet ports; a first seal located in said bore; a first pistonhaving a first cylindrical body located in said bore and engaging saidfirst seal, said first cylindrical body having a first end and a secondend, said first cylindrical body having an outwardly projecting lipadjacent said first end, a blind bore extending from said first endtoward said second end and a plurality of substantially radial openingsextending from the blind bore through said first cylindrical body;sleeve means having a cylindrical member with a first end and a secondend, said sleeve means being restrained in said bore, said first endengaging said first seal to substantially fix the position of said firstseal within said bore, said first seal, first piston and housingdefining a first chamber within said bore, said first chambercommunicating with said first inlet port via a first passage betweensaid first seal, said sleeve means and said second end of saidcylindrical body to allow fluid in said reservoir to flow into saidfirst chamber, said first chamber communicating with said first outletport, said cylindrical member having a bearing surface that contactssaid first piston to hold the first piston to hold the first piston insubstantially the axial center of said first chamber and a shoulderadjacent a second end; a second seal that engages said shoulder adjacentsaid second end of the cylindrical member of said sleeve means tosubstantially fix its position within said bore; a second piston havinga second cylindrical body located in said bore and engaging said secondseal, said second cylindrical body having a first end and a second end,said first end extending into said blind bore of said first piston, saidfirst piston, first seal, housing, second seal, and second pistondefining a second chamber within said bore, said second chambercommunicating with said second inlet via a second passage between saidsecond end of said cylindrical body and said second seal to allow fluidin said reservoir to flow into said second chamber, said blind borecommunicating with said second chamber through said plurality ofopenings in said first piston, said second chamber communicating withsaid second outlet port; and an input member responsive to an inputsignal for moving said first and second pistons with respect to saidfirst and second seals to interrupt fluid communication between saidreservoir and said first and second chambers and thereafter pressurizingthe fluid in the first and second chambers for providing said first andsecond outlet ports with pressurized fluid. .Iaddend..Iadd.
 27. Themaster cylinder, as recited in claim 26 wherein said master cylinderfurther includes:a first spring located between said first end of saidsleeve and said lip on said first cylindrical body for returning saidfirst piston to a first rest position in the absence of an input signalon said input member. .Iaddend..Iadd.
 28. The master cylinder, asrecited in claim 27 wherein said master cylinder further includes: asecond spring located in said blind bore of said first cylindrical bodyfor urging said second piston to a second rest position in the absenceof an input signal on said input member. .Iaddend..Iadd.
 29. A mastercylinder comprising: a housing having a bore therein, said housinghaving first and second inlet ports for connecting said bore to areservoir and first and second outlet ports; first and second sealslocated in said bore adjacent said first and second inlet portsrespectively; a sleeve located in said bore for substantially definingfixed positions for said first and second seals; a first piston locatedin said bore and engaging said first seal to substantially define afirst chamber, said first piston having a first end and a second end,said first chamber being connected to said first outlet port; a secondpiston located in said bore and engaging said second seal tosubstantially define a second chamber, said second piston having a firstend and a second end, said second chamber being connected to said secondoutlet port; a first passage located between said first end of saidfirst piston and said first seal; a second passage located between saidfirst end of said second piston and said second seal; retainer means forholding said second piston in said bore; spring means for urging saidfirst and second pistons toward said retainer means to allowsubstantially unrestricted fluid communication between said reservoirand said first and second chambers through said first and secondpassages, respectively; and input means responsive to an input force formoving said first and second pistons to terminate fluid communicationthrough said first and second passages and thereafter generate fluidpressure in said first and second chamber for distribution to said firstand second outlet ports. .Iaddend..Iadd.
 30. The master cylinder, asrecited in claim 29 wherein said first piston includes:a blind bore thatextends from said second end toward said first end, said blind borereceiving at least a portion of said second piston; and a radial outwardflange adjacent said second end. .Iaddend. .Iadd.
 31. The mastercylinder, as recited in claim 30 wherein said spring means includes: afirst spring located between said sleeve and said radial flange forurging said first end of said first piston toward said first sealwhereby fluid communication is established through said first passage;and a second spring located in said blind bore for urging said first endof said second piston toward said second seal whereby fluidcommunication is established through said second passage. .Iaddend..Iadd.
 32. A master cylinder comprising: a housing having a tapered boretherein, said housing having first and second compensator ports forconnecting said tapered bore to a fluid reservoir and first and secondoutlet ports connected to fluid pressure responsive devices; a sleevemember located in said tapered bore having a plurality of openingsthrough which fluid is communicated to said first outlet port; first andsecond seals associated with said sleeve member; bearing means engagingsaid sleeve member, said bearing means and sleeve member holding saidfirst and second seals in a substantially stationary position withinsaid bore while defining flow paths from the reservoir into said taperedbore; piston means having a first cylindrical member located in saidtapered bore by said bearing means and a second cylindrical member beinglocated in said tapered bore by a lip on said sleeve member, said firstand second cylindrical members engaging said first and second seals,respectively, and cooperating with said housing to define first andsecond chambers adjacent said first and second outlet ports,respectively, each of said first and second cylindrical members having afluted section located on the end thereof for defining an extension forsaid flow paths to allow fluid communication to the first and secondchambers, said second cylindrical member having a first diameter sectionand a second diameter section, said first diameter section having a lipon the peripheral surface thereof for engaging said sleeve member tohold the second diameter section in substantially the center of saidbore in said second chamber; a first spring located between said firstand second cylindrical members to establish the size of said firstchamber; a second spring located between said first cylindrical memberand said sleeve member for urging said first and second cylindricalmembers out of said first and second chambers toward a rest position;and input means responsive to an input force for moving said pistonmeans past said seals to interrupt communication between the reservoirand the bore and pressurizing the fluid in said first and secondchambers to supply the fluid pressure responsive devices with anoperational fluid pressure through said first and second outlet ports..Iaddend..Iadd.
 33. A master cylinder comprising: a housing having atapered bore therein, said housing having first and second compensatorports for connecting said tapered bore to a reservoir and first andsecond outlet ports; a sleeve located in said tapered bore; first andsecond seals positioned in said tapered bore adjacent said first andsecond compensator ports; bearing means cooperating with said sleeve tohold said first and second seals in a substantially stationary positionwithin said bore and to define flow paths adjacent each of said firstand second seals to connect the compensator ports with the tapered bore;piston means having first and second cylindrical members located in saidsleeve and engaging said first and second seals to define first andsecond chambers in the tapered bore, said sleeve holding said secondcylindrical member in the axial center of the tapered bore in the secondchamber; and input means responsive to an input force for moving thefirst and second cylindrical members past said first and second seals tointerrupt communication between the reservoir and the tapered borethrough said definite flow paths to allow further movement of the firstand second cylindrical members to pressurize the fluid in the first andsecond chambers and thereby supply the fluid pressure responsive deviceswith operational fluid through said first and second outlet ports..Iaddend.